Although water-soluble active ingredients realize excellent effects in the skin, they have a fatal disadvantage in that they cannot be absorbed transdermally. Therefore, it is difficult for a cosmetic composition containing such ingredients to realize their effects in the skin. This is because the skin has a multilayer structure with a hydrophobic base. Such a skin barrier function to water-soluble active ingredients may be overcome by using cosmetic instruments. However, since consumers don't like inconvenience of using cosmetic instruments, approaches using cosmetic instruments have not been positioned adequately in the cosmetic market despite excellent performance. Therefore, there is a need for developing a novel technology capable of delivering water-soluble active ingredients effectively to the skin without the aid of cosmetic instruments.
In 2000's, transdermal absorption technologies using iontophoresis stared to be suggested. The key of such technologies is allowing electric current to flow on the skin surface to induce iontophoresis so that water-soluble drugs may be introduced to the skin along the electric current. It has been reported that macromolecules such as proteins as well as water-soluble low-molecular weight drugs can be delivered through the skin. It has been already determined clinically in the cosmetic field that cosmetic instruments realizing an iontophoresis capacity increases skin absorption of water-soluble active ingredients and show their unique effects in the skin. However, there is a disadvantage in that such effects can be realized only by using instruments.
Use of piezoelectricity allows electric current to flow with no external power supply. Particularly, piezoelectric devices have been used in various forms in the display industry. Such devices are characterized in that electric current flows at a pressurized portion when pressure is applied thereto (e.g. a touch screen). The devices are systems in which structural deformation of a piezoelectric layer between two electrodes forms an electric dipole to induce generation of electric current.
The above information disclosed in the Background section is only for enhancement of understanding of the background of the invention and it may therefore contain information that does not form the prior art that is already known to a person of ordinary skill in the art.